The subject invention relates generally to an improved precharge pump for use with a controlled brake system.
Motor vehicle brakes that are interfaced with a controlled brake system are presently operated with hydraulic fluid. A master cylinder/booster distributes hydraulic fluid throughout the brake system as is well known in the art of hydraulic vehicle braking. Two separate feed lines transfer hydraulic fluid from the master cylinder to the driver""s side and passenger""s side brakes through a series of valves that are opened and closed by a controller. The controller determines which valves to open and close based on information obtained from sensors on the vehicle such as, for example, brake sensors, speed sensors, and yaw rate sensors.
The passenger""s side and the driver""s side hydraulic lines each include a main hydraulic pump for increasing hydraulic pressure in the hydraulic lines during a braking event. The appropriate valves either open or close depending upon whether a brake pedal is being depressed, or has been released. When the controller determines a controlled braking event is about to occur, it signals the main hydraulic pumps to rapidly increase pressure in the hydraulic lines for the valves to distribute hydraulic fluid to the appropriate brakes. However, the master cylinder alone has been found to be unable to supply enough hydraulic fluid to the main pumps to allow the main pumps to rapidly increase fluid pressure in the hydraulic lines. If the main pumps are not able to rapidly increase fluid pressure to the appropriate brakes, the effectiveness of the controlled brake system is significantly reduced. Therefore, a precharge pump is needed to rapidly supply additional hydraulic fluid to both the master cylinder and to the main pumps when signaled by the controller.
The precharge pump typically strokes one time when signaled by the controller that a controlled braking event is about to occur. This provides additional hydraulic fluid to the main pumps allowing the main pumps to rapidly increase fluid pressure to the valves. Complex gerotor or vane type pumps are often used for this type of application. These types of pumps have proven to be very costly and have not offered the reliability necessary to meet the requirements of the controlled brake assembly. Therefore, it would be desirable to introduce a low cost, mechanically simple pump to the controlled brake system for increasing the amount of hydraulic fluid to the main pumps to operate a controlled braking event.
The present invention is a precharge fluid pump for pumping hydraulic fluid through a controlled brake system. A housing defines a chamber that communicates with a hydraulic fluid circuit. A casing is fixedly attached to the housing and has an aperture aligned coaxially with the chamber. A piston includes a plunger slideably disposed within the chamber. A shaft is affixed to the plunger and has a distal end extending through the aperture. An armature is affixed to the distal end of the shaft. A coil is affixed to the casing and is arranged coaxially with the shaft. The coil generates a magnetic field through the armature when receiving an electrical current. The magnetic field draws the armature towards the casing driving the piston into the chamber for pumping hydraulic fluid. A spring biases the armature away from the casing in the absence of the magnetic field.
By using a magnet field to draw a piston into a pumping chamber for pumping hydraulic fluid into the hydraulic fluid circuit reduces the cost of the precharge pump. Further, this concept reduces the amount of moving parts commonly needed in a precharge pump, which increases the dependability of the controlled brake system.